Neuromuscular I

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Which component is primarily responsible for the striated appearance of muscle fibers?

Sarcoplasm

Epimysium

Myofibrils (correct)

Perimysium

What is the diameter range of skeletal muscle fibers?

30-60 micrometers

10-80 micrometers (correct)

5-20 micrometers

25-100 micrometers

In patients with Multiple Sclerosis, which symptom commonly follows paresthesias?

Pain in the back

Muscle hypertrophy

Weakness in a leg (correct)

Increased muscle tone

What surrounds the entire muscle and is composed of connective tissue?

Epimysium (B) Signup and view all the answers

Which process is hindered in individuals with Multiple Sclerosis due to its effect on the central nervous system?

Conduction velocity (B) Signup and view all the answers

What is the primary function of the sarcoplasmic reticulum in muscle fibers?

To store calcium ions (D) Signup and view all the answers

Which structural component of the sarcomere is responsible for the light zone appearance?

I band (D) Signup and view all the answers

What is the role of titin within the sarcomere?

To hold the actin and myosin filaments in place (C) Signup and view all the answers

How many myosin filaments are approximately found in each myofibril?

1500 (C) Signup and view all the answers

Which component acts as a regulatory unit in the actin filament structure?

Troponin (D) Signup and view all the answers

During contraction, which part of a sarcomere decreases in size?

I band (D) Signup and view all the answers

What structure allows nervous impulses to penetrate deep into the muscle fibers?

Transverse tubules (T tubules) (D) Signup and view all the answers

What is the diameter of actin filaments relative to myosin filaments?

About half the diameter of myosin filaments (A) Signup and view all the answers

What is the primary factor that determines the magnitude of the Nernst potential for an ion?

Ratio of specific ions on two sides of the membrane (D) Signup and view all the answers

What is the significance of membrane permeability in the context of membrane potential?

It determines the net diffusion rate of ions. (B) Signup and view all the answers

Which ion's concentration is greater inside a nerve cell compared to outside, contributing significantly to the resting membrane potential?

Potassium [K+] (A) Signup and view all the answers

What role does the sodium-potassium pump play in maintaining resting membrane potential?

It continually removes positive charge from the inside of the membrane. (B) Signup and view all the answers

How does the concentration gradient of sodium ions affect its diffusion potential?

It creates a strong inward diffusion tendency. (A) Signup and view all the answers

What is the consequence of failing to reach the threshold for depolarization in an action potential?

An action potential cannot be initiated. (D) Signup and view all the answers

What causes the negativity inside the nerve cell membrane during potassium diffusion?

The outflow of potassium ions. (B) Signup and view all the answers

What happens to the actin filaments during muscle contraction?

Actin filaments overlap with each other. (B) Signup and view all the answers

What is the primary function of the sodium-potassium pump after an action potential?

To restore resting membrane potential. (D) Signup and view all the answers

Which statement best describes the resting membrane potential?

It varies depending on the cell type. (C) Signup and view all the answers

Which type of refractory period allows for the possibility of generating another action potential with a stronger-than-normal stimulus?

Relative refractory period. (A) Signup and view all the answers

What role do calcium ions play in muscle contraction?

They activate troponin, facilitating the exposure of actin binding sites. (C) Signup and view all the answers

What occurs during the depolarization stage of an action potential?

A rapid increase in permeability to Na+ occurs (D) Signup and view all the answers

How does saltatory conduction enhance nerve transmission?

By enabling impulses to jump from node to node. (B) Signup and view all the answers

What is primarily responsible for the transient changes in membrane potential observed during impulse transmission?

Rapidly changing diffusion potentials. (D) Signup and view all the answers

Which step directly follows the cleavage of ATP by the myosin head?

The head tilts, initiating the power stroke. (B) Signup and view all the answers

Which statement accurately describes the function of voltage-gated sodium channels?

They transition from closed to open at approximately -55 mV (A) Signup and view all the answers

What effects does increasing the activity of sodium-potassium pumps have on a neuron's intracellular sodium level?

It decreases intracellular sodium levels. (A) Signup and view all the answers

What is the effect of a higher permeability to potassium ions compared to sodium ions on resting membrane potential?

It contributes to a negative membrane potential. (A) Signup and view all the answers

What is the immediate consequence of myosin binding to actin?

Myosin pulls actin towards the Z disks. (A) Signup and view all the answers

In what manner does current flow after an action potential is initiated?

It flows from the depolarized zone to adjacent areas. (B) Signup and view all the answers

Why does resting membrane potential change in response to stimuli?

It reflects changes in ion channel activity. (C) Signup and view all the answers

During which stage of the action potential do K+ ions rapidly diffuse out of the cell?

Repolarization stage (D) Signup and view all the answers

What is the function of the troponin-tropomyosin complex in muscle contraction?

To inhibit cross-bridge formation until calcium is present. (D) Signup and view all the answers

How much does potassium conductance increase during the latter stages of the action potential?

30-fold (B) Signup and view all the answers

What is the primary role of Schwann cells in the context of nerve impulses?

To insulate the axon with myelin sheaths. (B) Signup and view all the answers

Which process is primarily responsible for the energy supply during muscle contraction?

Hydrolysis of ATP by myosin heads. (A) Signup and view all the answers

What key feature of action potentials allows them to propagate along the length of the axon?

Localized depolarization triggering adjacent sodium channels. (C) Signup and view all the answers

What is the major difference in the conductance for K+ compared to Na+ in the resting state?

K+ conductance is 50-100 times greater than Na+ conductance (C) Signup and view all the answers

How does ATP affect the myosin head after a power stroke?

It causes the myosin head to detach from actin. (B) Signup and view all the answers

What initiates an action potential?

Stimulation from chemical, mechanical, or electrical sources (B) Signup and view all the answers

What occurs immediately after the myosin head tilts during the power stroke?

ADP and inorganic phosphate are released. (D) Signup and view all the answers

What happens to sodium channels after depolarization is complete?

They become inactive and close (B) Signup and view all the answers

What is the primary effect of increasing K+ permeability during repolarization?

It facilitates the return to resting membrane potential (D) Signup and view all the answers

Study Notes

Neuromuscular System I

This is a lecture on the neuromuscular system, part of a course called Applied Physiology (PT 8202).
The objectives include membrane potentials, action potentials, skeletal muscle structure, and skeletal muscle contraction.

Objectives

Membrane potentials and action potentials are crucial for nerve and muscle function.
Skeletal muscle structure and function are addressed, explaining the organization of muscle tissue from the whole muscle to individual muscle fibers.

Neuromuscular Domains

Motor units, fiber types, and EC coupling are related to neuromuscular structure and function.
Neuromuscular health/function and force generation interplay.
Bioenergetic and signaling properties of muscles are also discussed.

Membrane Potentials and Action Potentials

Net diffusion rate depends on membrane permeability, concentration gradient, electrical potential gradient, and pressure gradient, with electrical and concentration forces working at varying rates.
Electrical potentials exist across cell membranes.
These impulses transmit signals along nerves and muscles.
The Nernst potential is the potential difference that opposes net ion diffusion through a membrane. Magnitude relates to ion concentration ratios on each side of the membrane.

Diffusion Potentials

Membrane potentials are caused by ion differences (concentration gradients) across selectively permeable membranes.
Potassium is more concentrated inside nerve cells.
Sodium is more concentrated outside nerve cells.
These differences are key determinants of the resting membrane potential.

Diffusion Potentials - K+

Potassium ions tend to diffuse out of nerve cells due to their concentration gradient.
The outward flow of positive ions creates a negative potential inside the nerve fiber (-94 millivolts).

Diffusion Potentials - Na+

Sodium ions tend to diffuse into nerve cells due to their concentration gradient.
The inward flow of positive ions creates a positive potential inside the nerve fiber (+61 millivolts).

Resting Membrane Potential

The resting membrane potential is the electrical potential difference across the membrane of a nerve cell when it is at rest.
It depends on the concentration difference of ions across the membrane.
It is stabilized in dormancy by various channels & transporters that affect ion movement.
The permeability of different ion types is crucial in regulating the resting membrane potential. Specific ion permeabilities, such as potassium permeability, impact resting membrane values.
Various cell types have different resting membrane potentials. For example, skeletal muscle fibers have resting potentials between -85 to -95 mV.

Resting membrane potential

The resting membrane potential's stabilization involves potassium diffusion, sodium diffusion, sodium-potassium pumps, and contributions from chloride ions, with each playing a role in the membrane potential balance.
There are more potassium leak channels (100x) than sodium leak channels.
The sodium-potassium pump maintains the concentration gradient by pumping more sodium ions out of the cell than potassium ions into the cell.

Action Potentials

Rapid changes in membrane potential that propagate along nerve fibers.
Each action potential starts with a sudden change from resting negative potential, transitions to a positive potential then rapidly returns to negative potential.
This triggers a series of similar changes in adjacent areas, propagating the signal.
Depolarization leads to the opening of voltage-gated sodium and potassium channels.
Action potentials are all-or-nothing events.
The action potential's generation relies on exceeding a particular threshold voltage.

Action Potentials Stages

Resting stage, depolarization stage, repolarization stage, and hyperpolarization stage occur in sequences as a result of sodium and potassium channel dynamics.
The permeability for sodium rapidly increases, and then for potassium.
This interplay between sodium and potassium channels is key in defining and sustaining electrical signals.
Voltage-gated sodium and potassium channels are critical in the process of depolarization and repolarization during action potentials.

Refractory Period

A refractory period is a time period after an action potential during which it is difficult or impossible to fire another one, limiting the frequency of action potentials. This is due to inactivation of sodium channels, and the reestablishment of the resting potential.

Signal Transmission

Saltatory conduction is a mechanism of signal transmission in myelinated nerve fibers.
Schwann cells produce myelin sheaths around nerve fibers.
Myelin sheaths speed up signal transmission, leaping from node to node.

Saltatory Conduction

Action potentials are propagated from node to node in myelinated nerve fibers.
This allows for faster conduction velocity (5 to 50-fold) compared to non-myelinated nerve fibers.
Energy is conserved because depolarization events do not occur along every point of the neuron.

Conduction Velocity

Myelinated axons have faster conduction velocities compared to non-myelinated axons.
This difference impacts the speed of nerve impulses.

Clinical Application – Multiple Sclerosis

MS is an immune-mediated demyelinating disease of the central nervous system (CNS).
Patients with MS experience a range of symptoms, including paresthesia, weakness, and vision problems that vary in presentation (ranging by affected area of the brain/spinal cord).

Skeletal Muscle Structure

Muscle, fascicle, muscle fiber are components progressively organized in hierarchical fashion in skeletal muscles.
Muscle fibers contain units called myofibrils, and myofibrils have sarcomeres arranged end-to-end.
Muscle fibers are composed of myofibrils that are arranged in parallel.
Myofibrils/sarcomeres are composed of thin (actin) and thick (myosin) filaments.

Myofibrils

The contractile elements of skeletal muscle.
Contain contractile proteins (actin and myosin).
Exhibit a striated appearance.

Sarcomere

The smallest functional unit of a skeletal muscle fiber.
Consists of inter-related components (I band, A band, H zone, Z disk and M-line.)
Actin (thin) and myosin (thick) filaments structure sarcomeres.

Titin

A large structural protein in sarcomeres that helps stabilize the positions of myosin and actin filaments and acts as a spring which helps return the muscle to its resting length.
This is important for muscle mechanics and function.
Plays an important structural role.

Sarcomere: Protein Filaments

Myosin and actin filaments are crucial parts of the contractile machinery of a muscle fiber.
Myosin: is the thick filament, comprising about 60% of muscle protein, appears dark, and includes 1500 myosin filaments per myofibril.
Actin: is the thin filament, comprises about 3000 filaments per myofibril, contains three structural proteins, and appears lighter.
These proteins interact for muscle contraction to occur.

Myosin (Thick Filaments)

Each myosin molecule is composed of six polypeptide chains (2 heavy chains, 4 light chains).
The arrangement of subunits forms twisted filaments with globular heads.
The heads have sites for interaction with actin and energy expenditure.

Actin (Thin Filaments)

Actually comprised of multiple proteins (G-actin, tropomyosin, troponin), each with a specific function associated with muscle contraction.
The actin filament is organized.
Tropomyosin regulates access to the active site of actin.
Troponin complex (troponin C, T, I) involved with Ca2+ ions is key to activating the muscle's active sites.

Actin & Myosin Relationship

Actin and myosin interaction is central for muscle contraction.
The relationship's dynamic involves proteins, ions, and energy to manage movement.

Sliding Filament Mechanism

Relaxed state, contracted state, sliding filament mechanism concepts are presented. This is the mechanism of muscle contraction.
Calcium, ATP, and myosin, and actin interaction are central to the process.
Energy (ATP) is required to fuel the muscle contraction process.

Skeletal muscle structure: sliding filament mechanism

The process of muscle contraction, including the role of ATP, calcium, myosin head movement, actin and myosin binding sites, and ATP hydrolysis
Regulatory proteins to help control the interaction.

The Sliding Filament Model

Explains how muscle contraction occurs by the interaction of actin and myosin filaments.
Contraction is achieved by the sliding of actin filaments over the myosin filaments.
During muscle contraction (or shortening), the I band and H zone shorten. Only the A band remains unchanged.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your knowledge on the anatomical features of muscle fibers and the effects of Multiple Sclerosis. This quiz covers key concepts such as muscle structure and common symptoms related to neurological disorders. Perfect for students studying health sciences or anatomy.